[compiler-rt] [libcxx] [libcxxabi] [libunwind] [runtimes][PAC] Harden unwinding when possible (PR #143230)

[Oliver Hunt via llvm-commits]

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@@ -103,10 +104,68 @@
 #define _LIBCXXABI_DTOR_FUNC
 #endif
 
-#if __cplusplus < 201103L
-#  define _LIBCXXABI_NOEXCEPT throw()
-#else
-#  define _LIBCXXABI_NOEXCEPT noexcept
+#if __has_include(<ptrauth.h>)
+#  include <ptrauth.h>
 #endif
 
+#if __has_extension(ptrauth_qualifier)
+
+// The actual value of the discriminators listed below is not important
+// beyond their impact on ABI. The derivation of the constants is only
+// being included for the purpose of maintaining a record of how they
+// were originally produced.
+
+// ptrauth_string_discriminator("__cxa_exception::actionRecord") == 0xFC91
----------------
ojhunt wrote:

The only actual reason for the "this was the origin" is to clarify that these weren't arbitrary - essentially providing provenance if anyone is _really_ curious. It's really not important (these aren't used for cryptography, where the origin of any constant is important, but we started doing this out of habit a while back for all those we could still find the original derivation on principle)

https://github.com/llvm/llvm-project/pull/143230